docs: def get_foldrate(seq, secstruct):
      """Submit sequence and structural class to FOLD-RATE calculator (http://www.iitm.ac.in/bioinfo/fold-rate/)
      to calculate kinetic folding rate.
  
      Args:
          seq (str, Seq, SeqRecord): Amino acid sequence
          secstruct (str): Structural class: `all-alpha``, ``all-beta``, ``mixed``, or ``unknown``
  
      Returns:
          float: Kinetic folding rate k_f
  
      """
  
      seq = ssbio.protein.sequence.utils.cast_to_str(seq)
  
      url = 'http://www.iitm.ac.in/bioinfo/cgi-bin/fold-rate/foldrateCalculator.pl'
  
      values = {'sequence': seq, 'eqn': secstruct}
      data = urlencode(values)
      data = data.encode('ASCII')
      response = urlopen(url, data)
  
      result = str(response.read())
      ind = str.find(result, 'The folding rate,')
      result2 = result[ind:ind + 70]
      ind1 = str.find(result2, '=')
      ind2 = str.find(result2, '/sec')
      rate = result2[ind1 + 2:ind2]
  
      return rate